The present invention relates to an inflator securing structure for securing a substantially cylindrically-shaped inflator to a retainer in an airbag system. More specifically, it relates to an inflator securing structure in which the inflator has a fixed shaft having a substantially D-shaped cross section projecting at its one end along the axial direction thereof, and the fixed shaft is engaged in a substantially D-shaped locking hole provided in a retainer, thereby allowing the inflator to be secured to the retainer so that the inflator is substantially unrotatable about its axis. The present invention also relates to an airbag system in which the inflator is secured to the retainer by means of the inflator securing structure.
For the purposes of the present invention, the sentence “the inflator is substantially unrotatable about its axis” means that the inflator is somewhat rotatable by a degree of clearance (play) between the flat surface on the circumference of the fixed shaft and the chordal side of the locking hole when the fixed shaft is engaged in the locking hole.
An airbag system installed on a passenger seat side or the like in a motor vehicle includes an airbag and an inflator for inflating the airbag. The airbag and the inflator are secured to a retainer.
The inflator has a substantially cylindrical shape and includes a gas exhaust port provided at its circumference along the longitudinal axis thereof.
As a cylindrically-shaped inflator securing structure, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 5-65048) describes an inflator securing structure in which an inflator has a fixed shaft having a substantially D-shaped cross section projecting at its one end along the axial direction thereof, the cross section being perpendicular to the axial direction of the inflator, and the fixed shaft is engaged in a substantially D-shaped locking hole provided in a retainer, thereby allowing the inflator to be secured to the retainer.
Patent Document 1 describes that, when the fixed shaft is engaged in the locking hole, a flat circumferential surface of the fixed shaft and a chordal side of the locking hole symmetrically face each other, thereby allowing the inflator to be secured to a retainer with a gas exhaust port oriented toward a predetermined direction so that the inflator is substantially unrotatable about its axis.
The inflator securing structure described in Patent Document 1 has a predetermined clearance (play) created for design purposes between the circumference of the fixed shaft and the inner circumference of the locking hole. This clearance allows the inflator to be rotatable about its axis by the degree of that clearance.
Generally, the clearance between the flat surface on the circumference of the fixed shaft and the chordal side of the locking hole is approximately 0.5 mm when the fixed shaft is engaged in the locking hole. The allowable range of the resultant play in the rotational direction of the inflator, namely, angular tolerance is +/− 3 through 5 degrees.
With the recent reduction in size of airbag systems, there has been a tendency toward using an inflator with a smaller diameter. The use of such inflator results in a reduction in diameter of a fixed shaft provided on the inflator. Although the diameter of a locking hole is dependent on the diameter of the fixed shaft, there must be almost the same clearance created for design purposes between the fixed shaft and the locking hole regardless of whether the fixed shaft has a larger diameter or not. For this reason, the fixed shaft with a smaller diameter relatively produces a greater clearance between the fixed shaft and the locking hole relative to the diameter of the fixed shaft, resulting in a greater degree of rotation of the fixed shaft inside the locking hole. Accordingly, the fixed shaft with the smaller diameter may cause inflator to create play greater than a predetermined rotational tolerance range.
Accordingly, the objective of the present invention is to provide an inflator securing structure which allows an inflator to play in the rotational direction within the predetermined rotational tolerance range even when a fixed shaft with a smaller diameter is employed, as well as an airbag system which includes the inflator secured to a retainer by means of the inflator securing structure.
Further objects and advantages of the invention will be apparent from the following description of the invention.